DROP FUNCTION statement

Syntax

DROP FUNCTION function-name

Identifies
the particular function to be dropped, and is valid only if there is exactly
one function instance with the function-name in the schema. The identified
function can have any number of parameters defined for it.

An error will occur in any of the following circumstances:

If no function with the indicated name exists in the named or implied schema
(the error is SQLSTATE 42704)

If there is more than one specific instance of the function in the named or
implied schema

If you try to drop a user-defined function that is invoked in the
generation-clause of a generated column